The present invention relates to crane mechanisms and, more particularly, to crane mechanisms adapted for use on tow trucks and other similar vehicles and structures.
Mobile cranes associated with wrecker trucks for towing other vehicles, for example which are utilized for lifting and transporting heavy loads from inaccessible places, have generally employed mechanical winches in conjunction with a boom for lifting and positioning a load. The maximum safe load limit for these mechanical arrangement is generally determined by, for example, the mass of the material used in the mechanical devices, cable diameters, thicknesses of structural steel for the boom and supports therefor, sizes of bolts and pivots, etc. A mobile crane using a hydraulic actuated boom is disclosed in U.S. Pat. No. 4,993,911, the entire disclosure which in incorporated by reference herein.
Generally, crane designs of the prior art utilize a single boom and winch arrangement for lifting or towing a heavy load. Thus, a load is secured either by a hook or other attachment mechanism at one point on the load, or by a chain or other attachment mechanism wrapped around the load and secured to the boom's one or more cables. Thus, the entire load is lifted from an end of one boom.
Such an arrangement makes manipulation of the load difficult. For example, it is difficult for a wrecker having a single boom configuration to lift and upright an overturned truck or rail car in a controlled manner. While mechanical wreckers are known having double booms, these are generally unsuitable for lifting and manipulating heavy loads. Typically, the booms were configured to swivel from side to side and were raised and lowered by mechanical means, for example by hand cranks.